Nitride-based light-emitting diode device

ABSTRACT

A nitride-based light-emitting diode (LED) device includes an n-type nitride semiconductor layer, an active layer that is disposed on the n-type nitride semiconductor layer, a p-type nitride semiconductor layer disposed on the active layer, and a defect control unit disposed between the n-type nitride semiconductor layer and the active layer. The defect control unit includes first, second and third defect control layers that are sequentially disposed on the n-type nitride semiconductor layer in such order, and that have different doping concentrations. The third defect control layer includes one of Al-containing ternary nitride, Al-containing quaternary nitride, and a combination thereof.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a bypass continuation-in-part application ofInternational Application No. PCT/CN2019/074127 filed on Jan. 31, 2019,which claims priority of Chinese Invention Patent Application No.201810470874.1 filed on May 17, 2018. The entire content of each of theInternational and Chinese patent applications is incorporated herein byreference.

FIELD

The disclosure relates to a semiconductor optoelectronic device, andmore particularly to a nitride-based light-emitting diode (LED) device.

BACKGROUND

A nitride-based light-emitting diode (LED) is among one of thesemiconductor solid-state light emitting devices that can directlyconvert electricity into light using a semiconductor p-n junction as thelight emitting material. A conventional LED generally includes asubstrate, and an n-type nitride semiconductor layer, a stress releaselayer, an active layer, an electron blocking layer and a p-type nitridelayer that are sequentially disposed on the substrate in such order.

The stress release layer includes multiple pairs of an InGaN layer and aGaN layer that are alternately stacked on one another. The stressrelease layer is usually formed with several V-shaped defects (pits) atlow temperature to release stress in LED device. The V-shaped defectsare initially induced by a lattice mismatch and a large difference ofthermal expansion coefficients between a sapphire substrate and a GaNepitaxial layer (i.e., n-type nitride semiconductor layer), and then theresultant dislocations propagate to form the V-shaped defects in thestress release layer. Since the size and density of the V-shaped defectsare random and uncontrollable, distribution of electrons and holeswithin the LED device would be non-uniform, resulting in electricleakage and efficiency droop, thereby affecting the quantum yield of theLED device.

SUMMARY

Therefore, an object of the disclosure is to provide a nitride-basedlight-emitting diode (LED) device that can alleviate or eliminate atleast one of the drawbacks of the prior art.

According to the disclosure, the nitride-based LED device includes ann-type nitride semiconductor layer, an active layer, a p-type nitridesemiconductor layer, and a defect control unit.

The active layer is disposed on the n-type nitride semiconductor layer.The p-type nitride semiconductor layer is disposed on the active layeropposite to the n-type nitride semiconductor layer.

The defect control unit is disposed between the n-type nitridesemiconductor layer and the active layer, and includes a first defectcontrol layer, a second defect control layer and a third defect controllayer that are sequentially disposed on the n-type nitride semiconductorlayer in such order, and that have different doping concentrations. Thethird defect control layer includes one of Al-containing ternarynitride, Al-containing quaternary nitride, and a combination thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the disclosure will become apparent inthe following detailed description of the embodiments with reference tothe accompanying drawings, of which:

FIG. 1 is a schematic view illustrating a first embodiment of anitride-based light-emitting diode (LED) device of this disclosure, andan energy band diagram of a third defect control layer of the firstembodiment;

FIG. 2 is a schematic view illustrating a variation of the firstembodiment of the nitride-based LED device and an energy band diagram ofthe third defect control layer thereof;

FIG. 3 are atomic force microscopic images illustrating the topographyof a conventional LED device (left image) and that of the firstembodiment of the nitride-based LED device, respectively (right image);and

FIG. 4 is a schematic view illustrating a fourth embodiment of thenitride-based LED device according to the disclosure.

DETAILED DESCRIPTION

Before the disclosure is described in greater detail, it should be notedthat where considered appropriate, reference numerals or terminalportions of reference numerals have been repeated among the figures toindicate corresponding or analogous elements, which may optionally havesimilar characteristics.

Referring to FIG. 1 , a first embodiment of a nitride-basedlight-emitting diode (LED) device according to the present disclosureincludes a substrate 100, an n-type nitride semiconductor layer 200, adefect control unit 300, an active layer 400, and a p-type nitridesemiconductor layer 500.

The substrate 100 may be made of a material suitable for epitaxialgrowth, which may include, but is not limited to, sapphire, silicon(Si), silicon carbide (SiC), zinc oxide (ZnO), gallium nitride (GaN),and aluminum nitride (AlN).

The n-type nitride semiconductor layer 200 is formed on an upper surfaceof the substrate 100. In certain embodiments, the n-type nitridesemiconductor layer 200 may be made of GaN doped with an n-typeimpurity, such as Si, Ge, Sn, and Pb. In other embodiments, the n-typenitride semiconductor layer 200 may be an unintentionally doped GaNlayer.

The nitride-based LED device may further include a buffer layer 110disposed between the substrate 100 and the n-type nitride semiconductorlayer 200 for reducing a lattice mismatch therebetween. There are noparticular limitations on the material for making the buffer layer 110,as long as the buffer layer 110 is capable of being lattice matched withthe substrate 100. Examples of such material of the buffer layer 110 mayinclude, but are not limited to, AlN, GaN, AlGaN, and combinationsthereof. In certain embodiments, the buffer layer 110 is a compositestructure that includes several layer pairs alternately stacked on oneanother, each of the layer pairs has two layers made of differentmaterials as mentioned above.

The active layer 400, which is a region for radiative recombination ofelectrons and holes, is disposed on the n-type nitride semiconductorlayer 200 opposite to the buffer layer 110. The active layer 400includes multiples layer pairs, each layer pair including a potentialbarrier layer and a potential well layer. The potential barrier layersand the potential well layers in the active layer 400 are alternatelystacked. The potential barrier layer may be made of GaN, AlGaN, orAlInGaN. The potential well layer may be made of InGaN.

The p-type nitride semiconductor layer 500 is disposed on the activelayer 400. The p-type nitride semiconductor layer 500 may be doped witha p-type impurity, such as Mg, Ca, Sr, Ba, and combinations thereof. Inthis embodiment, the p-type nitride semiconductor layer 500 is dopedwith Mg, and serves to provide holes.

The nitride-based LED device may further include an electron blockinglayer 510 disposed between the active layer 400 and the p-type nitridesemiconductor layer 500 for preventing electron overflow.

The defect control unit 300 is disposed between the n-type nitridesemiconductor layer 200 and the active layer 400. The defect controlunit 300 includes a first defect control layer 310, a second defectcontrol layer 320, and a third defect control layer 330 that aresequentially disposed on the n-type nitride semiconductor layer 200 insuch order, and that have different doping concentrations.

The defect control unit 300 serves to control the size and density ofV-shaped defects 340 which are formed due to the lattice mismatchbetween the substrate 100 and the n-type nitride semiconductor layer 200(see FIG. 3 ), and to prevent loss of the antistatic property of thenitride-based LED device, so as to improve the injection efficiency ofholes, thereby improving the quantum yield of the nitride-based LEDdevice.

Specifically, the first defect control layer 310 may be made of amaterial selected from the group consisting of GaN, InGaN, AlGaN,InAlGaN, and combinations thereof. In this embodiment, the first defectcontrol layer 310 is a low temperature-grown n-type GaN layer forcontrolling the depth of the V-shaped defects 340. By adjusting thethickness, the doping concentration and growth temperature of the firstdefect control layer 310, the depth of the V-shaped defects 340 can bewell controlled, so as to increase the injection efficiency of holes.For example, the first defect control layer 310 may be doped with ann-type impurity, and the n-type doping concentration of the first defectcontrol layer 310 is lower than that of the n-type nitride semiconductorlayer 200. In certain embodiments, the n-type doping concentration ofthe first defect control layer 310 ranges from 1×10¹⁷/cm³ to 5×10¹⁸/cm³.The first defect control layer 310 may have a thickness ranging from 50Å to 5000 Å.

The second defect control layer 320 is made of a material selected fromthe group consisting of GaN, InGaN, AlGaN, InAlGaN, and combinationsthereof. In this embodiment, the second defect control layer 320 is ann-type GaN layer, i.e., doped with an n-type impurity. In certainembodiments, the n-type doping concentration of the second defectcontrol layer 320 is greater than that of the first defect control layer310, and is lower than that of the n-type nitride semiconductor layer200. For example, then-type doping concentration of the second defectcontrol layer 320 ranges from 1×10¹⁷/cm³ to 1×10¹⁹/cm³. Thus, the seconddefect control layer 320 is capable of improving the reduced antistaticproperty of the nitride-based LED device caused by the V-shaped defects340 (i.e., enhancing the antistatic capability thereof). The seconddefect control layer 320 may have a thickness ranging from 10 Å to 1000Å.

The third defect control layer 330 includes Al-containing ternarynitride, Al-containing quaternary nitride, or a combination thereof. Incertain embodiments, the third defect control layer 330 is one of anAl-containing nitride superlattice structure and an Al-containingnitride monolayer structure.

In this embodiment, the third defect control layer 330 is anAl-containing ternary nitride superlattice structure which includesmultiple pairs of layers, each of which contains a first layer (e.g.,Al-containing layer) and a second layer (e.g., Al-free layer) which hasa band gap lower than that of the first layer. The first layers and thesecond layers in the Al-containing ternary nitride superlatticestructure are alternately stacked. As shown in the energy band diagramof FIG. 1, each pair of the third defect control layer 330 has aperiodical change of band gap. For example, each pair of theAl-containing ternary nitride superlattice structure contains the firstlayer represented by Al_(a1)Ga_(1-a1)N, and the second layer representedby In_(e1)Ga_(1-e1)N, and 0<a1≤0.3, and 0<e1≤0.3. Alternatively, eachpair of the Al-containing ternary nitride superlattice structure maycontain the first layer represented by Al_(a2)In_(1-a2)N, and the secondlayer represented by In_(c1)Al_(1-c1)N, and 0<a2≤0.3, and 0<c1≤0.3.

In certain embodiments, the third defect control layer 330 is doped withan n-type impurity, and the doping concentration of the third defectcontrol layer 330 is lower than those of the first defect control layer310, the second defect control layer 320, and the n-type nitridesemiconductor layer 200. For example, the third defect control layer 330may have a doping concentration ranging from 1×10¹⁷/cm³ to 1×10¹⁸/cm³,and may have a thickness ranging from 100 Å to 5000 Å.

Based on the above, the relationship of the n-type doping concentrationamong the first defect control layer 310, the second defect controllayer 320, the third defect control layer 330 and the n-type nitridesemiconductor layer 200 may be described as follows: the dopingconcentration of the nitride semiconductor layer 200 is greater thanthat of the second defect control layer 320, the doping concentration ofthe second defect control layer 320 is greater than that of the firstdefect control layer 310, and the doping concentration of the firstdefect control layer 310 is greater than that of the third defectcontrol layer 330.

Since the third defect control layer 330 includes Al-containing ternaryand/or quaternary nitride (e.g., the Al-containing ternary nitridesuperlattice structure in this embodiment, i.e., doping Al therein), thedensity and size of the V-shaped defects 340 may be increased (see rightimage of FIG. 3 ), as compared to that of the stress release layer(i.e., multiple pairs of an InGaN layer and a GaN layer) of theconventional LED device (see left image of FIG. 3 ). As such, the holesmay be injected into the active layer 400 from a side wall of theV-shaped defects 340, so as to increase the injection efficiency ofholes. By virtue of the Al-containing ternary nitride superlatticestructure that includes the first and second layers respectively havinghigh and low band gaps, the electron migration rate and electronoverflow in the nitride-based LED device can be reduced, andrecombination of the electrons and holes within the active layer 400 canbe improved, so as to enhance the quantum yield of the nitride-based LEDdevice and reduce efficiency droop.

In this embodiment, the nitride-based LED device is formed with a mesastructure 210 which is exposed from the n-type nitride semiconductorlayer 200, and which may be formed by etching from the p-type nitridesemiconductor layer 500 to the n-type nitride semiconductor layer 200.The nitride-based LED device further includes a first electrode 220 thatis formed on the mesa structure 210, and a second electrode 530 that isformed on a mesa structure of the p-type nitride semiconductor layer500. The first electrode 220 may be made of a material selected from thegroup consisting of Ti, Al, Au, and combinations thereof. The secondelectrode 530 may be made of chromium/gold (Cr/Au).

The nitride-based LED device may further include a p-type ohmic contactlayer 520 disposed between the p-type nitride semiconductor layer 500and the second electrode 530 for reducing an impedance therebetween. Thep-type ohmic contact layer 520 may be made of a material selected fromthe group consisting of nickel/gold laminate, indium tin oxide (ITO),and zinc oxide (ZnO).

When an electric current flows through the active layer 400 via thefirst electrode 220 and the second electrode 530, the electrons whichmigrated from the n-type nitride semiconductor layer 200 and the holeswhich migrated from the p-type nitride semiconductor layer 500 canundergo recombination in the active layer 400, so as to allow the activelayer 400 to emit light.

Referring to FIG. 2 , in a variation of the first embodiment, when thesubstrate 100 is made of GaN or Si, the mesa structure 210 is not formedto expose the n-type nitride semiconductor layer 200, and the firstelectrode 220 is disposed on the substrate 100 opposite to the n-typenitride semiconductor layer 200.

A second embodiment of the nitride-based LED device is similar to thefirst embodiment, except that in the second embodiment, the third defectcontrol layer 330 is an Al-containing quaternary nitride superlatticestructure which includes multiple pairs of layers. The layers in eachpair contain a first layer represented by Al_(x1)In_(y1)Ga_(1-x1-y1)Nand a second layer represented by Al_(m1)In_(z1)Ga_(1-m1-z1)N. The firstlayers and the second layers in the Al-containing quaternary nitridesuperlattice structure are alternately stacked, and 0<x1≤0.3, 0<y1≤0.3,0<m1≤0.3, and 0<z1≤0.3, with the proviso that x1 is different from m1,or y1 is different from z1.

A third embodiment of the nitride-based LED device according to thepresent disclosure is similar to the first embodiment, except that inthe third embodiment, the third defect control layer 330 is anAl-containing nitride superlattice structure which includes anAl-containing ternary nitride and an Al-containing quaternary nitride,and which includes multiple pairs of layers. The layers in each paircontain a first layer including Al-containing quaternary nitride, and asecond layer including Al-containing ternary nitride. The first layersand the second layers in the Al-containing nitride superlatticestructure are alternately stacked. For example, the first layer may berepresented by Al_(x2)In_(y2)Ga_(1-x2-y2)N and the second layer may berepresented by In_(m2)Ga_(1-m2)N, and 0<x2≤0.3, 0<y2≤0.3, and 0<m2≤0.3.In certain embodiments, the first layer is represented byAl_(x3)In_(y3)Ga_(1-x3-y3)N, and the second layer is represented byIn_(z3)Al_(1-z3)N, and 0<x3 ≤0.3, 0<y3≤0.3, and 0<z3≤0.3. In otherembodiments, the first layer is represented byAl_(x4)In_(y4)Ga_(1-x4-y4)N and the second layer is represented byAl_(1-z4)GaN, and 0<x4≤0.3, 0<y4≤0.3, and 0<z4≤0.3.

Referring to FIG. 4 , a fourth embodiment of the nitride-based LEDdevice according to the present disclosure is generally similar to thefirst embodiment, except that in the fourth embodiment, the third defectcontrol layer 330 is an Al-containing ternary nitride monolayerstructure, which includes one of AlGaN and InAlN. Alternatively, thethird defect control layer 330 may be an Al-containing quaternarynitride monolayer structure, which includes AlInGaN.

In summary, by virtue of the defect control unit 300 disposed betweenthe n-type nitride semiconductor layer 200 and the active layer 400, thedensity and size of the V-shaped defects 340 formed inside thenitride-based LED device can be controlled. That is, the depth of theV-shaped defects 340 can be controlled by the first defect control layer310, the reduced antistatic capability of the nitride-based LED devicecaused by the V-shaped defects 340 can be improved by the second defectcontrol layer 320, and the density of the V-shaped defects 340 can becontrolled by the third defect control layer 330. As such, the injectionefficiency of the holes can be increased, while the electron migrationrate, the electric overflow, and the efficiency droop effect can beeffectively reduced, so as to improve the distribution uniformity ofelectrons and holes in the active layer 400, thereby enhancing thequantum yield of the nitride-based LED device of this disclosure.

In the description above, for the purposes of explanation, numerousspecific details have been set forth in order to provide a thoroughunderstanding of the embodiments. It will be apparent, however, to oneskilled in the art, that one or more other embodiments may be practicedwithout some of these specific details. It should also be appreciatedthat reference throughout this specification to “one embodiment,” “anembodiment,” an embodiment with an indication of an ordinal number andso forth means that a particular feature, structure, or characteristicmay be included in the practice of the disclosure. It should be furtherappreciated that in the description, various features are sometimesgrouped together in a single embodiment, figure, or description thereoffor the purpose of streamlining the disclosure and aiding in theunderstanding of various inventive aspects, and that one or morefeatures or specific details from one embodiment may be practicedtogether with one or more features or specific details from anotherembodiment, where appropriate, in the practice of the disclosure.

While the disclosure has been described in connection with what areconsidered the exemplary embodiments, it is understood that thisdisclosure is not limited to the disclosed embodiments but is intendedto cover various arrangements included within the spirit and scope ofthe broadest interpretation so as to encompass all such modificationsand equivalent arrangements.

What is claimed is:
 1. A nitride-based light-emitting diode (LED)device, comprising: an n-type nitride semiconductor layer; an activelayer disposed on said n-type nitride semiconductor layer; a p-typenitride semiconductor layer disposed on said active layer opposite tosaid n-type nitride semiconductor layer; and a defect control unitdisposed between said n-type nitride semiconductor layer and said activelayer, and including a first defect control layer, a second defectcontrol layer and a third defect control layer that are sequentiallydisposed on said n-type nitride semiconductor layer in such order, andthat have different doping concentrations, wherein said third defectcontrol layer includes one of Al-containing ternary nitride,Al-containing quaternary nitride, or a combination thereof; and whereineach of said first defect control layer, said second defect controllayer, and said third defect control layer is doped with an n-typeimpurity; and the doping concentration of said n-type nitridesemiconductor layer is greater than that of said second defect controllayer, the doping concentration of said second defect control layer isgreater than that of said first defect control layer, and the dopingconcentration of said first defect control layer is greater than that ofsaid third defect control layer.
 2. The nitride-based LED device ofclaim 1, wherein said third defect control layer is one of anAl-containing nitride superlattice structure and an Al-containingnitride monolayer structure.
 3. The nitride-based LED device of claim 2,wherein said third defect control layer is an Al-containing ternarynitride superlattice structure which includes multiple pairs of layers,said layers in each pair containing a first layer represented byAl_(a1)Ga_(1-a1)N and a second layer represented by In_(e1)Ga_(1-e1)N,said first layers and said second layers in said Al-containing ternarynitride superlattice structure being alternately stacked, and 0<a1≤0.3,and 0<e1≤0.3.
 4. The nitride-based LED device of claim 2, wherein saidthird defect control layer is an Al-containing ternary nitridesuperlattice structure which includes multiple pairs of layers, saidlayers in each pair containing a first layer represented byAl_(a2)In_(1-a2)N and a second layer represented by In_(c1)Al_(1-c1)N,said first layers and said second layers in said Al-containing ternarynitride superlattice structure being alternately stacked, and 0<a1≤0.3,and 0<c1≤0.3.
 5. The nitride-based LED device of claim 2, wherein saidthird defect control layer is an Al-containing ternary nitride monolayerstructure, which includes one of AlGaN and InAlN.
 6. The nitride-basedLED device of claim 2, wherein said third defect control layer is anAl-containing quaternary nitride superlattice structure which includesmultiple pairs of layers, said layers in each pair containing a firstlayer represented by Al_(x1)In_(y1) Ga_(1-x1-y1)N and a second layerrepresented by Al_(m1)In_(z1) Ga_(1-m1-z1)N, said first layers and saidsecond layers in said Al-containing quaternary nitride superlatticestructure being alternately stacked, and 0<x1≤0.3, 0<y1≤0.3, 0<m1≤0.3,and 0<z1≤0.3, with the proviso that x1 is different from m1, or y1 isdifferent from z1.
 7. The nitride-based LED device of claim 2, whereinsaid third defect control layer is an Al-containing quaternary nitridemonolayer structure, which includes AlInGaN.
 8. The nitride-based LEDdevice of claim 2, wherein said third defect control layer is anAl-containing nitride superlattice structure which includesAl-containing ternary nitride and Al-containing quaternary nitride. 9.The nitride-based LED device of claim 8, wherein said Al-containingnitride superlattice structure includes multiple pairs of layers, saidlayers in each pair containing a first layer represented byAl_(x2)In_(y2)Ga_(1-x2-y2)N and a second layer represented byIn_(m2)Ga_(1-m2)N, said first layers and said second layers in saidAl-containing nitride superlattice structure being alternately stacked,and 0<x2≤0.3, 0<y2≤0.3, and 0<m2≤0.3.
 10. The nitride-based LED deviceof claim 8, wherein said Al-containing nitride superlattice structureincludes multiple pairs of layers, said layers in each pair containing afirst layer represented by Al_(x3)In_(y3)Ga_(1-x3-y3)N and a secondlayer represented by In_(z2)Al_(1-z3)N, said first layers and saidsecond layers in said Al-containing nitride superlattice structure beingalternately stacked, and 0<x3≤0.3, 0<y3≤0.3, and 0<z3≤0.3.
 11. Thenitride-based LED device of claim 8, wherein said Al-containing nitridesuperlattice structure includes multiple pairs of layers, said layers ineach pair containing a first layer represented byAl_(x4)In_(y4)Ga_(1-x4-y4)N and a second layer represented byAl_(1-z4)GaN, said first layers and said second layers in saidAl-containing nitride superlattice structure being alternately stacked,and 0<x4≤0.3, 0<y4≤0.3, and 0<z4≤0.3.
 12. The nitride-based LED deviceof claim 8, wherein each of said first defect control layer, said seconddefect control layer and said third defect control layer is doped withan n-type impurity; and the doping concentration of said n-type nitridesemiconductor layer is greater than that of said second defect controllayer, the doping concentration of said second defect control layer isgreater than that of said first defect control layer, and the dopingconcentration of said first defect control layer is greater than that ofsaid third defect control layer.
 13. The nitride-based LED device ofclaim 1, wherein said first defect control layer is made of a materialselected from the group consisting of GaN, InGaN, AlGaN, InAlGaN, andcombinations thereof.
 14. The nitride-based LED device of claim 1,wherein said second defect control layer is made of a material selectedfrom the group consisting of GaN, InGaN, AlGaN, InAlGaN, andcombinations thereof.